For those that are overweight yes, but not everyone that has sleep apnea is overweight (like me). The apneas are caused by different things in different people and I believe any surgical solution would likewise depend on the person.

It usually helps, but as with most obesity-linked conditions it's not suitable on its own as a first-line treatment. The effect is small compared to CPAP, and sufficient weight loss to see that effect takes months, whereas CPAP starts working literally overnight (DME/insurance shenanigans notwithstanding).

Also, chronic sleep disruption is associated with a cluster of symptoms (impaired insulin sensitivity, lethargy, increased hunger) that make it very difficult to lose weight in a normal/healthy way. Many patients find that they lose 10-20 pounds after starting CPAP with no conscious change in their lifestyle.

OSA can be caused by many factors. Weight is only one. I'm skinny and I'd be dead without CPAP.

Generally yes, because the throat is less constricted when you're not overweight.